This patch updates the libxenctrl calls in Qemu to use the new interface,
otherwise Qemu wouldn't be able to build against new versions of the
library.

We check libxenctrl version in configure, from Xen 3.3.0 to Xen
unstable.
Signed-off-by: NAnthony PERARD <anthony.perard@citrix.com>
Signed-off-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: NAlexander Graf <agraf@suse.de>
Signed-off-by: NAlexander Graf <agraf@suse.de>